Method for ink pressure modulation in a printer for axially symmetric objects

ABSTRACT

An ink pressure modulation method is presented in a direct-to-shape printing system for applying images on the exterior of an axially symmetrical media object that has a contoured, varying exterior surface, such as occurs on curved wine bottles and sports equipment like bats. The method varies ink pressures based on the movement positions of each print head as they move over the surface of the media object. A movement-based formula is presented to allow for continuous updating of pressures in ink tank manifolds to allow independent changes in pressure to each inkjet print head during printing.

This application claims the benefit of filing priority under 35 U.S.C. §119 and 37 C.F.R. § 1.78 of U.S. provisional Application Ser. No.62/830,864 filed Apr. 8, 2019, for a Printing System for Applying ImagesOver a Contoured Axially Symmetric Object. All information disclosed inthat prior pending nonprovisional application is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates generally to printing of images onarticles of manufacture. In greater particularity, the present inventionrelates to printing images on the exterior of axially symmetricalarticles of manufacture using inkjet printing technology. The inventionalso relates to direct printing on cylindrical objects while the objectsare axially rotated, and to some degree “direct-to-shape” printing orDTS for 3-dimensional objects.

BACKGROUND OF THE INVENTION

Several techniques are utilized to print images on manufactured goods,such as drink and cosmetics containers. These containers are made ofvarious materials, such as plastics, metals, and coated paper, and thetraditional method for placing images on these containers, sometimescalled “imaging” a container, is to print a label on a plastic or papersubstrate and then affix the pre-printed label onto the container withadhesive. However, during the last 20 years many manufactures havetransitioned from label printing to direct printing onto the containersurface, sometime referred to as “direct-to-shape” (DTS) printing.However, while a label is a flexible medium and may be printed usingtraditional flexible sheet printing using methods going back over 100years, direct printing on containers poses many challenges. Onechallenge is that while paper readily absorbs and retains inks and is awell understood medium for imaging, the containers themselves are madeof materials that are difficult to image. Inks of special chemicalblends and additives must be used, sometimes in the presence of activedrying or hardening processes such as catalyst exposure or fast-curingusing ultra-violet (UV) radiation. Further, container shapes are fixed,and an imaging process must take into account the irregular and variedshapes of the containers that are to be imaged. Such challenging printsurfaces comprise a good-many products, such as drink cans and bottles,home care products, cups, coffee tumblers, personal care items,automotive parts, sports equipment, medical products, and electronicscontainers to name just a few. Hence, choosing the proper type of DTSprinting equipment largely depends on the shape, size, number of colors,and type of substrate to be imaged, as well as the method that ispreferred in which to transfer the image onto the substrate surface.

Various techniques have been developed to achieve DTS printing. Onetechnique, “pad printing,” allows the transfer of a two-dimensionalimage onto a three-dimensional surface through the use of a siliconepad, an ink cup, and an etched plate. Pad printing is ideal fordifficult substrates such as products found in the medical field andpromotional printing, but due to the expense of the process pad printingtypically uses only 1 or 2 colors during a print job.

Another technique, screen printing utilizes a mesh or screen to transferthe ink to the substrate surface. The process requires creating a screenthat selectively permits ink to flow through the screen using a blockingstencil. While a photographic process may be used to create a screen,and hence allows relatively good resolution of imaging, the processrequires substantial set-up time and is less flexible because any updateor small alteration to the image to be laid down requires the creationof a new screen set. In addition, screen printing is typicallyrestricted to only 1 or 2 colors because each color requires its ownseparate customized screen.

Inkjet DTS printing has over time risen to be a preferred method for DTSprinting, especially for package printing. Inkjet printing utilizes adigital printhead to print full color customized designs in one ormultiple imaging passes and may be applied directly to the substratesurface of the object or medium. Developed in the 1970s, inkjet printerswere created to reproduce a digital image on a printing surface. Thetransfer occurs by propelling droplets of ink directly onto thesubstrate medium. The ink delivery mechanism is called the “printhead,”and is controlled by a digital image held by a connected computer systemand which may be altered an infinite number of times. However, thedesign of printheads in an inkjet system varies greatly. Each head isuniquely designed for its application, and a variety of digital printersdesigns are available to be used to print on various substrates. Hence,various factors drive the types of inkjet printing system to be utilizedfor a printing project, such as the type of product substrate to beprinted, the volume of products to be printed, and the requiredmanufacturing speed for the imaging of any product traversing throughthe manufacturing line.

However, the benefits of inkjet printing in DTS applications have drivena recent preference to use inkjet systems in product manufacturinglines. For example, inkjet printing requires less set-up time and allowsfor faster print and cure times. Inkjet printing also is configurable toallow printing on multiple items at once, whereas other printing methodsare often restricted to a single print instance for each object beingprinted. Moreover, print jobs do not require fixed setup time and costs,such as the generation of screens or the installation of plates.

On great advantage of inkjet printing is the ability to change graphicimages quickly, sometimes almost in real-time, to adjust for printingresults. Modern imaging software is template driven and allows for theimportation of new or re-worked graphics instantly. Hence, theflexibility of image alteration on a job-by-job basis is a distinctadvantage.

In addition, inkjet printers are robust enough to be used for short andlong printing production projects, thereby meeting various manufacturingdemands. For example, single machine may be used to prototype or providea sample, low-volume job for a potential client, or that same machinemay be used in the same facility to print thousands of articles in aday. Further, the same machine may use various types of inks toaccommodate different object substrate materials.

Finally, conveyor and assembly line capability allow the inkjet printingprocess to become automated which can increase productivity and lowerlabor costs. So-called “inline” printers can do such printing atincredibly fast production rates. Typically, the inkjet printheadremains stationary while the substrate is moved past the printhead. Thistype of inkjet system is ideal for barcoding and dating productpackaging. Single-pass multi-color inkjet printers are similar sometimesoffering higher quality imaging with more color options at slightlyslower print speeds.

One type of inkjet system is specialized to print on the surface ofcylindrical containers and are called “digital cylindrical presses.” Forexample, The INX Group Ltd. (aka “Inx Digital” and “JetINX”) a divisionof Sakata INX offers a cylindrical printing solution under its CP100 andCP800 line of direct-to-shape (i.e. DTS) inkjet printing systems. Thesesystems allow for the creation of an inkjet production line to printdirectly onto axially symmetrical objects. Other companies offer similarsystems, such as Inkcups Now Corporation which offers the Helix line ofDTS printers. These printers use a rotatable mandrel to hold an objectand rotate the object next to an inkjet printhead as the printhead jetsink onto the surface of the cylindrical object. An image is captured fortransfer onto an object and a printing “recipe” created, either by theprinting machine itself or separately on personal computer and thenimported into the printing machine. The “recipe” includes informationnecessary for the printing an image onto a media object and the recipeparameters are specific to each type of printer utilized.

The CP100 machine is a good example of an industry standard cylindricalDTS printing system. The system is a stand-alone machine that performsnon-contact printing of images on generally cylindrical objects,particularly hollow cylindrical objects or hollow partially-cylindricalobjects, for example, cans and bottles and including two-piece cans andbottles. Each cylindrical object is hand-loaded onto the machine andsecured by vacuum on a mandrel to prevent slippage, which is part of acarriage assembly that functions to linearly positioning the objectbeneath at least one digitally controlled inkjet printhead. The objectis rotated in front of the printhead while ink is deposited to theobject to produce a desired printed design on the object. The ink iseither partially or fully cured immediately after printing by exposingthe ink to an energy-emitting means, such as a UV light emitter,positioned directly beneath the object. A carriage assembly is fixedlymounted to a linear slide actuator, which is in turn fixedly mounted toa mounting frame, whereby the carriage assembly is free to traversealong the linear slide actuator. The carriage linearly advances theobject in a position adjacent to the inkjet printhead such that a firstportion of the object may be printed if the object length is longer thanthe length of the printhead. The object is rotated while thecomputer-controlled printheads deposit ink from a supply of ink locatedabove the object being printed upon. Simultaneously the UV light emittereither partially or completely cures the ink. The carriage thencontinues to advance the can further such that the entire length of thecan is printed. As may be understood, the continuous advancement of theobject by the printhead may not be necessary if the printhead is longerthan the image desired to be printed on the object. The image itselfcomprises a digital image that is imported from a separate imagingapplication and loaded into application that creates a “recipe” of theimage based on the physical specifications of the object to be printedupon. The profile is loaded through an operating system present on themachine and utilized to control motion of the object held by thecarriage assembly along the linear slide. A print engine running on themachine controls the delivery of ink onto the object via the inkjetprinthead as the object is moved past the printhead in a digitallycontrolled manner. The precise deposition of the ink via the inkjetheads onto the object, is dependent upon the object recipe whichincludes the specific amount and color of ink applied to the object asit traverses the printhead. The structure and operation of standardcylindrical DTS printing systems are fairly well understood in theprinting industry and disclosed in representative U.S. Pat. No.6,918,641B2 and U.S. Pat. No. 7,967,405B2.

However, the machines offered by Inx International only print onto acylindrically flat exteriors and do not allow for the printing overcurved exteriors of axially symmetric objects, such as exists on tapereddrink tumblers or 3-dimensionally contoured bottle shapes.

The above-mentioned Helix line of cylindrical printers offered byInkcups does allow for DTS printing of axially symmetrical, tapereddrinkware, such as common stainless-steel drink tumblers. The Helixprinter achieves this by tilting a mandrel holding the object to beprinted and adjusting the angle of the object relative to a stationaryprinthead to approximate a straight line over a contoured surface of theobject. The problem with the Helix approach is that such straight-lineapproximation does not ensure a constant density of ink to be applied tothe object because the print head moves outside of an optimal jettingdistance due to the fixed length of the print head. This non-optimalpositioning of the object in relation to the printhead results inunacceptable color shifts in the printed image and various image issuesdue to increased ink drop drift and overspray. Since these types ofcylindrical printers cannot provide constant articulation of the head ormedia throughout the print cycle to minimize the jetting distance, theHelix and similar printers are limited to printing on axis symmetricalshapes that are approximately cylindrical or conical where the gapbetween the printhead and printed surface can be maintained at adistance that does not exceed the capability of the printhead to provideacceptable dot placement and image quality. Hence, these types ofprinters are limited in the types media on which they may print becausemost contoured media objects will exceed the printhead capabilities ofthese printers (e.g. greater than 5 mm jetting distances), thereby notbeing able to produce a quality image.

Therefore, which is needed is a system including a method forcontrolling ink jet print pressures that allows for inkjet printingalong a 3-dimensionally contoured surface of an object duringdirect-to-shape or DTS imaging that provides superior color imaging overa contoured surface where approximating the shape as a cylinder or conedoes not provide acceptable image quality due to the printhead being toofar away from the continually varying printed surface.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an ink pressuremodulation method in a direct-to-shape printing system for applyingimages on the exterior of an axially symmetrical media object that has acontoured, varying exterior surface, such as occurs on curved winebottles and sports equipment like bats. The method varies ink pressuresbased on the movement positions of each print head as they move over thesurface of the media object. A movement-based formula is presented thatallows for continuous updating of pressures in ink tank manifolds toallow independent changes in pressure to each inkjet print head duringprinting.

Other features and objects and advantages of the present invention willbecome apparent from a reading of the following description as well as astudy of the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A printing system incorporating the features of the invention isdepicted in the attached drawings which form a portion of the disclosureand wherein:

FIG. 1 is a front perspective view of the printing system showing themajor elements of the machine;

FIG. 2A is a perspective view of the printing system having the exteriorenclosure panels removed to show the internal operative components;

FIG. 2B is a magnified perspective view of the printing area of theprinting system;

FIG. 3 is a front side elevational view of the printing system;

FIG. 4 is a magnified view of the front left portion of the printingsystem;

FIG. 5 is a detail view of the carriage mounting assembly of theprinting system shown in FIG. 1;

FIG. 6 is a major subassembly perspective view of the printing area ofthe printing system;

FIGS. 7A-7B show front and back perspective views of the headmanipulators for the printing system;

FIG. 8 is an enlarged perspective view of the top portion of theprinting area for the printing system;

FIG. 9 is a rear elevational view of the left side of the printingsystem showing internal electrical components in an electrical bay;

FIG. 10 is a detail view of a bank of ink head assemblies positionedalong a contoured surface of a media object being printed;

FIG. 11 is a diagram showing the print head movement relative to themedia object movement while being imaged;

FIG. 12 is a top-level software control diagram showing the relationshipbetween the machine operating system and control signals sent toelectronic control systems;

FIG. 13 is a function diagram showing the flow of control signalsbetween various elements of the motion control subsystem of the printingsystem; and,

FIGS. 14A-14B are an example CAM profile table based on a print jobprofile.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings for a better understanding of the function andstructure of the invention, FIG. 1 shows a front view of the machine 10showing the primary external components of the invention. Machine 10includes an external frame 11 and a series of adjustable rollers 12supporting the machine components. Multiple panel doors 13 provide areasfor storage of printer supplies, such as large volume ink reservoirs,and for cable conduit distribution for internal communications and powerlines to power the machine 10. A pair of accordion doors 16 havingviewing windows as shown to provide for the isolation of moving partsduring the printing process for safety reasons, while allowing viewingof images being applied to various types of media within the interiorprinting area 17. Frame 11 also supports a top panel 21 having multiplefans with exterior grills for exhausting of heated air within themachine and any chemical fumes created during the imaging and curingprocess. A hood 19 supported by frame 11 and connected with top panel 21extends to the right of the machine 10 over a media fixing area 18. Anarticulated support arm assembly 22 is connected to top panel 21 andallows for an operator to place a laptop or other compatible personalcomputing device on a platform landing area 23 of the arm to facilitatecommunication and control of the machine if needed. Landing area 23 canalso hold a display device and keyboard for communicating with a WindowsPC held behind panels 13 that controls printer 10.

System 10 incorporates several purchased subsystems that includeintegration modifications to make system 10 operative. For example,system 10 includes an ink delivery system manufactured by INX Group Ltd.(aka JetINX) that includes a system of pumps, electronic controls (i.e.a print engine), and a tubing system to transport inks of various colorsfrom reservoirs inside a user accessible lower portion in the rear ofthe system 10 to a plurality of ink tanks and thereafter to a bank ofinkjet print heads, as will be further described. The INX print engineincludes its own human machine interface (HMI) that runs on a standardWindows based PC and that controls the operation of the print engine.Some variations of the INX HMI include the capability to vary inkpressures delivered to each inkjet head by sending messages to the INXHMI through a dynamic linked library (.DLL) file loaded onto the PC. Inthe preferred embodiment of the herein described printing system 10, asecond HMI (referred to herein as the “LSINC HMI”) overlays the INX HMIto extend the interface capabilities of the INX HMI such the hereindescribed system may utilize the INX supplied sub-systems. Inparticular, the LSINC HMI responsive to a supplied media object geometryfile converts those media geometries into a form usable by a motioncontrol subsystem and using those geometries transfers ink pressurechanges to the INX HMI to adjust for inkjet print head movements, aswill be further discussed. Further, as is known in the industry, inksare selected specifically to bond with and adhere to the surface ofvarious types of media object surfaces in order to accommodate thegraphical color requirements of each graphic design used in a print job.The complexities of selecting inks and color coordination to achieve aparticular graphic design goal, and the elements for and the operationof the purchased INX ink delivery system will be omitted in as much assuch information is understood in the industry and not necessary for acomplete understanding of the herein described invention.

FIGS. 2A-2B and FIG. 3 show the machine internal components including anexhaust fan 24 supported by frame 11 and protruding through panel 21, aprinting assembly area 25 within printing area 17 supported by internalframe components 11 and positioned above and surrounding a space intowhich media is positioned for imaging. To the left of the printingassembly area 25 is positioned a collection of peristaltic pumps in asingle assembly 27 supported above an electronics bay 28 holding variouselectronics and printed circuit boards (PCBs) for controlling themachine and printing process. The left side 26 of machine 10 houses thepumps and electronics bay and is accessible from both the front and backof machine 10. Exhaust fan 24 removes waste heat from area 26 to keep aconstant flow of cooler air flowing across individual components.

FIGS. 2B-3 show the individual component assemblies in interior printingarea 17 from FIG. 1. Printing assembly area 25 includes banks of inkhead assemblies 29 supported above printing area 17, and a lineargrouping of ink curing lamps 32 are positioned along a lower portion ofprinting area 17 for curing of inked images. Positioned above assemblies29 are multiple ink supply tanks 31 feeding each ink head assembly viatubing (not shown). Adjacent to each tank is a control board 34 forcontrolling the operation of each printing head manipulator assembly inthe bank 29.

From the front side of bay 26 may be more clearly seen per FIG. 4 theseries of peristaltic pumps 38 above several PCBs. Electronics bay 28includes an encoder I/O board 41, a vacuum control board 42 forcontrolling the pressure of ink flowing from each pump 38 to ink headassemblies 29, and a USB controller board 43 adjacent to twoconsolidated I/O boards 44.

Referring now to FIGS. 5 and 6 it may be seen an arrangement of elementsthat causes a printable media object 51 to be secured and moved into theimaging area 17 from media loading area 18 responsive to electroniccontrol elements held in bay 26. Initially a piece of media, such as anobject having an axially symmetrical surface area, is clamped at itsends between two clamping fixtures 52 a,b with the help of a mediasupport member 56. Clamping fixtures 52 a,b form a rotatable mandrelholding object 51 rotatable via internal bearings at each end whichallow media 51 to freely rotate about its longitudinal central axis viarotary servo 53 causing axial rotation responsive to inputs receivedfrom electronics held in bay 26. In this arrangement, object 51 alongwith clamps 52 a,b effectively becomes a spindle the surface of whichbecomes a printable surface during rotation. A carriage 57 supports theservo motor, media, and the spindle arrangement which is slidable backand forth 69 from the media loading area 18 into printing area 17responsive to control inputs from a pair of control knobs 58.Critically, as carriage 57 travels inward under assemblies 29, its axialorientation remains fixed so that a target distance between the surfaceof object 51 and each ink print head is maintained during rotation,which comports with the surface features of object 51 which has anaxially symmetric shape. An adjustable tailstock member 59 assists tokeep object 51 positioned statically with respect to the object'slongitudinal axis by providing an adjustable means to maintain object 51locked within a single rotating axis while clamped in the slidablespindle arrangement.

Once locked with clamping fixtures 52 a,b, carriage 57 is moved intointerior printing area 17 and underneath print head assemblies 29.Carriage 57 is further adapted to be slidable in a precise andcontrolled manner along the object's longitudinal axis along path 68once repositioned in printing area 17. Printer head banks 29 are heldfixed in relation to object 51 with a head manipulator mount 65supported by upper and lower frame rails 11 a,b. Mount 65 includes apair of end members 66 a,b slidable supported by railing 11 b. A headmanipulator alignment adjuster 67 permits fine adjustment of mount 65 byrotating screws 67 a,b. The combination of the carriage 57 andsupporting rails and brackets described allows for a relatively precisestarting position for calibration of the print assemblies 29 relative toobjects 51 placed within printing area 17 prior to controlled movementof the individual print head assemblies as will be described.

Below object 51 positioned in movement path 68 are positioned an inkcuring assembly 60 holding a serial bank of curing lamps 63 locatedbelow object 51 so that light emitted by lamps 63 blanket the surface ofobject 51 during rotation with ultraviolet radiation (UV). This causesinks being applied via print head assemblies 29 to cure during afraction of a rotation of object 51. Assembly 60 includes a plurality ofcuring lamp assemblies 62 each holding a stepper motor 64 that allowsfor fine adjustment of curing lamp height relative to object 51 as itmoves along path 68 during rotation. As shown, bracket 61 a supportslamp assemblies 62 which is slidably supported by two pairs of framerails 61 b,c.

Referring now to FIGS. 7A-7B it may be seen the arrangement of elementsin each print head manipulator assemblies 71 held by ink head assemblybank 29. Each head manipulator 71 is supported by mount 65 in slidablerelation via horizontal rails 84 a,b. A pair of stepper motors 82 areheld by back plate 78 at the upper most part of plate 78 and oriented sothat their output shafts 81 extend downward along the outer surface ofplate 78. Shafts 81 are rigidly bolted to the tops of columns 76supported by a pair of vertical rails 79 slidably bolted to the outersurface of plate 78 via fixtures 75. At the bottom of columns 76 a printhead support platform 73 is held by a pair of freely rotating screws 77that act as pivot points to allow the independent movement of columns 76up and down relative to one another responsive to actions of steppermotors 82. This allows for independent pivoting movement 74 of platform73. Each platform 73 holds a print head 72 from which ink may bedeposited on the surface of object 51 just below platform 73, and due tothe pivoting movement of platform 73 print head 72 is also caused topivot about surface of object 51 responsive to actions of stepper motors82.

Importantly, entire backplate 78 is movable horizontally along path 86due to it being slidably supported by horizontal rails 84 a,b. A stepperactuator 83 is attached to and supported by head manipulator mount 65and connected via a shaft 87 to side bracket 85 which is fixed to oneside of the rear surface of back plate 78. Since horizontal rails 84 a,bslidably support backplate 78 to mount 65 (see FIG. 6), movement ofshaft 87 by actuator 83 allows for precise horizontal movement of headmanipulator 71 along path 86 responsive to electronic impulses issued byelectronics held by bay 26 and driver control boards 34.

Referring to FIGS. 8-9, above ink head assemblies 29 is positioned 6dual well ink reservoirs or tanks 31 holding various ink colors asrequired for each imaging job and connected via tubes (not shown) toeach ink print head 72 through fittings 88. A series of driver boards 34are positioned adjacent to tanks 31 and together with carriage controlboards 91 control movement of media object 51 and print heads 72 duringprinting. A suitable driver board for drivers 34 is the A-CSD series ofstepper motor drives (Part No. CSD ET 94) offered by R.T.A. MotionControl Systems located in MARCIGNAGO (PV), Italy.

From the rear side of machine 10 driver boards 34 and carriage controlboards 91 are positioned to the left of electronics bay 26. Bay 26includes additional PCBs to control movement during printing such as, arotary servo drive board 92 to control rotary servo 53, a linear axisservo drive board 93 to control horizontal movement of head assemblies71 and an EtherCAT controller board 94 to control communications betweeneach driver board from a machine operating system. A power supply rack96 provides power to the electronics for machine 10 and is positioned toallow for air below the machine to be passed over components 96 and outof exhaust port 24 in top panel 21.

Referring now to FIGS. 10 and 11, it may be seen the manner and movement100 of ink heads 72 to conform to the surface of media object 51 as itrotates 108 within printing area 17. As shown media object 51 includesan axially symmetric surface area that varies by radius R_(i) 119 fromcentral axis 107 of object 51, thereby creating a print path 122 havinga print length of L 117 along the curve which is parallel to targetmedia surface 121, but spaced away from surface 121 by a small amountrepresenting the space or “offset” 126 between an ink print head 72lower surface 105 and object surface 121. This distance is small,typically 0.80 mm to 1.0 mm, and is the distance that ink droplets musttraverse prior to landing on object surface 121 to create an image. Acontoured media object having an axially symmetrical surface willpresent a contoured surface portion 102 to the extent that R_(i) 119varies from axis 107, thereby creating a fixed local slope M_(i) 116along lower surface 105 for the width 123 of each print head that variesas each print head 72 traverses along media surface 121 in print headpath 122. As print head bank 29 adjusts to the surface 121 of media 51within a contour 102, a plurality of ink heads, for example 103, 104,and 106, alter their angle by pivoting around pivot path 74 (see FIG.7A) to match the slope M_(i) at each R_(i) along surface 121 so thatoffset 126 is minimized. During rotation 108 of object 51, for eachR_(i) along surface 121 ink head lower surface 105 is positioned acorresponding distance Z_(i) from axis 107.

Any image to be printed is rotated into a portrait orientation with ay-axis value assigned to its height and an x-axis value assigned to itswidth. These x and y values become the dimensions X and Y, where Y isalong the height and X wraps around the media. As may be understood, foreach Y_(i) there is a corresponding radius R_(i). Depending upon thelength of any image to be printed and the length of media surface 121upon which the image is to be applied, print path 122 has a fixed lengthL 117 that object 51 must be moved using carriage 57 along path 68 (seeFIG. 6) and having a precise location Y_(i) 114 along axis 107. A seriesof equations is shown below that prescribes the slope or angle intowhich each print head 72 must move in order to suitably conform to apredetermined print path 122 at each Y_(i) position 114 with itscorresponding radius R_(i). Such a print path may also be referred to asa “motion path.”

Given the following variables, a motion path may be calculated:Vl _(i) =V _(carriage) +dVl _(i)dVl _(i)=path length mm/1 mm horizontal travel*V _(carriage)mm/sdVl _(i)=(√{square root over ((R _(i+1) −R _(i))²+(Y _(i+1) −Y_(i))²)}−(Y _(i+1) −Y _(i)))×Vcarriage

A localized slope may be calculated:

$M_{i} = {\frac{dRi}{dYi} = \frac{{R\left( {i + 1} \right)} - {Ri}}{{Y\left( {1 + 1} \right)} - {Yi}}}$

The position of the printhead midpoint is defined as:Zl _(i) =R _(i)+(Offset)cos(arctan(M _(i)))

Approximation of print path length difference from Y_(total):l _(i)=Σ_(i=0) ^(n) dl _(i)=Σ_(i=0) ^(n)(√{square root over ((R _(i+1)−R _(i))²+(Y _(i+1) −Y _(i))²)}−(Y _(i+1) −Y _(i)))

The relative position “Y” of print head to carriage position is:U _(i) =l _(i)+(Offset)sin(arctan(M _(i))

This control strategy holds to within 10% accuracy for contour angles upto 25 degrees, but steeper angles require smaller steps, or athree-point path length approximation that assesses the impact ofY_(i−1), Y_(i), Y_(i+1) on arc thru R_(i−1), R_(i) & R_(i+1). It will benoted that based on the ratio of the print surface slope to the headslope, image quality degradation can be predicted and a determinationmade as to whether printed image quality will be acceptable for anobject's particular contour characteristics.

In addition, image quality can be improved by reducing the local printhead width through the reduction of nozzles used in each print head. Forexample, to maintain image quality, an imaging objective is to limit inkjet drop-on-drop misalignment to less than ¼ of a drop. The drop sizeand resolution are chosen such that they blend together between imagelines creating full coverage. On contoured surfaces the width of theprint head (width 123) represents a chord length along contour profile102. Approximating the contour as a series of tangent continuous arcs,one can compare the chord length printed on the surface to the length ofthe contour profile 102 represented by the following formula:s=r*theta

where s=the length of the arc, r=the radius of the arc, and thetarepresents the swept angle of the arc. The objective is to maintain thedifference between arc length s and the print head's print width, (W),to be less than ¼ of the image line spacing, which approximates to:1/(image resolution along arc×4)

Where,s−W<0.25/(image resolution along arc)

For a given W and resolution, s−W may be calculated to be:2r(arcsin)(W/2r)−W.

As may be seen, by reducing the printed ink width W expressed from aprint head results in a decrease in the radius of curvature that may beprinted with acceptable image quality. This results in the ability toprint over a contoured object with a higher degree of slope (i.e. atighter curve) without degrading image quality. Hence, using thesevalues the print head width may varied to adjust the image quality toaccommodate differing contour properties for various media objects.

Independent of image quality in relation to ink head width, becauseobject 51 is moved at a constant horizontal velocity “V” 127 ink heads72 must independently move in a horizontal direction independently fromcarriage 57 motion because each print head along any contour area 102will encounter a different local slope M_(i) for its print path at anyparticular moment along that path. This is accomplished by activatingstepper 83 (see FIG. 7B) to move shaft 87 in a bilateral horizontaldirection 86 to maintain a constant relative velocity of each print headmanipulator 71 along axis 107 as carriage 57 moves along path 68. Thismovement of ink heads independent of carriage movement holding mediaobject 51 is important to allow for a consistent printed image alongcontour 102 without distortion.

Because contour 102 presents an increased or decreased R_(i) dependingupon the surface shape of media 51, an image having a fixed width X andheight Y uses a predetermined amount of ink for a particular image foran area X×Y, as will be understood. Because R_(i) varies, in order foran image to be placed on a contoured object surface the amount of inkmust also be varied in order to avoid over inking the surface for anyR_(i) that is less than the maximum R_(i) on the object surface. Hence,a gradient mask must be generated as part of a profile for any imagingjob in order to proportionately reduce the amount of ink in response tothe degree of contour present on the object 51. This is accomplished byutilizing a third-party illustration software application, such as forexample Adobe Illustrator, to create a separate drawing layer for theimage artwork to be applied to the media object 51. The separate layer(e.g. called a “knockout” layer) is created as the top most layer usinga “process white” that will not actually cause ink to be jetted. Itreduces the opacity of all lower levels by its presence. The targetreduction is created by applying a gradient opacity to this layer. Thegradient starts at 1% of ink removal at the largest diameter andincreases per the following equation at each position in the artworkwith a corresponding R_(i) diameter:Knockout percentage at a given position=(1−(media diameter atposition)/(max media diameter))×100%These values are saved in the image file that is processed through araster image processor or “RIP” to create a printer specific file fortransfer to the PC controlling the print job prior to execution of theprint, as will be further discussed job.

Precise control of motion of several elements in machine 10 allow forthe precise application of ink onto the surface of object 51. This isachieved by driver boards sending signals to several actuators in acoordinated manner. The signals sent by those driver boards arecontrolled by a CAM table, such as a CAM profile function, defined by aset of X and Y coordinates. Those X and Y coordinates are derived fromthe equations shown above and are unique for each print job. An exampleCAM table disclosing suitable example variable values is shown in FIGS.14A-14B, as will be further discussed.

All control signals from driver boards to control motion in machine 10are initiated from a Windows based O/S software control system run by aPC housed underneath printing area 17, with display screen connected tothe Windows OS held by platform 23. Print initiation occurs from signalssent by the PC to motion controller 191 which then controls a series ofmotion means as part of a motion control subsystem 170 (see FIG. 13) viaan EtherCAT communications system 179. Alternatively, they could besupplied by a non-Windows operating system with the properconfiguration.

Referring to FIG. 12, a software control system 140 includes Windows OS141 running on PC 142 having suitable storage 148, display output anduser control elements 151, and output communications means as iscommonly available in modern PCs. Computer storage 148 holdsconfiguration files and library files 143 (e.g. DLL files) to enablesystem 140 to utilize loaded files from a print job profile generationprocess 146 that provides input into system 140 to operate printersystem 10 for a print job. Process 146 includes the generating of animage/graphic file for printing onto media 51, and the generation of ageometry file that includes geometric information corresponding to thesurface configuration of the media object onto which the image will beapplied in the system 10. The image file includes color and ink levelreduction values referred to herein as a “gradient mask” for reducingthe amount of ink released responsive to surface contour values. Theprint job profile is held in PC storage 148 as a set of files 143 loadedonto PC and utilized by HMI applications loaded in memory 150. Akeyboard and display 151 allow for the generation of a human machineinterface (HMI) for an operator 152 to initiate and monitor a print joband for the loading of media onto the machine through loading area 18.As mentioned above, the LSINC HMI overlays the INX HMI and replicatesand extends the capabilities of the INX HMI and the LSINC HMI is theinterface that a human operator 152 utilizes.

As previously indicated, each print job comprises a specific “recipe”for each media object to be printed that includes the geometry of thesurface of the object and an image to be applied to the exterior surfaceof the object. The herein described recipe is specific for system 10 andholds information not usable by prior printing systems. In practice, agraphic artist would create or obtain an image in a raster file format(i.e. a bitmap image), such as a jpeg, tiff, or png (portable networkgraphics) formats that they desire to be printed on the media object 51.That image is then converted into a vector-based image through the useof an illustration software application, such as for example AdobeIllustrator. The above-mentioned “gradient mask” is created using thisillustration application as well as creating a vector output file, suchas an Adobe Postscript file, that may be utilized by a raster imageprocessor (“RIP”) for actually printing the final image. The output fromAdobe Illustrator may also produce a vector-based pdf (portable documentformat) file which is an acceptable format for a RIP to utilize. As isknown, a raster image processor produces a raster image for output toprinting hardware, such as inkjet printing hardware, that produces theimage on print media. A RIP is preferred to control the printinghardware because a high-level page description language, such as in apdf file format, may be utilized where specific image control may beobtained over the final printed image, such as printing resolutions, inklimits, and color calibrations. One acceptable RIP software applicationis ONYX RIP available from Onyx Graphics, Inc. located in Salt LakeCity, Utah. The print file created by ONYX RIP is an .isi file type thatseparates color planes. This .isi file is supplied directly to the INXsupplied print engine 149 for printing.

Print engine subsystem 149 is comprised of a software and hardwarecomponent. The software component, principally characterized by the INXHMI, resides on the PC and breaks up the received .isi file into printswaths which are transferred via a USB connection to the head drivecontroller 191 (see FIG. 13). The head drive controller 191 thencommunicates the color data to the respective head drives to cause theprint heads to print at an appropriate position and timing to print animage on the media. The timing of the firing and motion is synchronizedthrough an encoder signal 172 (see FIG. 13) with the firing slaved tothe encoder signal generated by motion control subsystem 170 (see FIG.13). Further discussions regarding the timing, color control, andprinting head actuation of print heads 72 in system 10 shall be omittedin as much as such printing methodologies are standard, purchasableitems and well understood for digital printing in the printing industryand not necessary for a complete understanding of the herein describedinvention.

In addition to the .isi print file, a set of geometry valuesrepresentative of the media object 51 are loaded onto the print systemPC 142 and saved on PC storage system 148 as part of two files 143necessary for each print job for each type of media object 51 to beprinted upon. That geometry file is a simple comma separated variablelisting representative of measurements of the media object 51, such as aradius value from the asymmetrical radial axis to the surface of themedia along its length, the overall length of the media, the maximumwidth of the media, etc. The geometries may be generated in variousknown ways, such as for example a human operator taking physicalmeasurements of the media, a scanning program scanning the media andgenerating geometries of the media, or a CAD program generating thosegeometric values. The LSINC HMI reads the media geometry file stored asa .lsg file and creates a CAM table (see FIGS. 14A-14B) for controllingthe movement of the inkjet printing heads and for calculating inkpressure adjustment values. That CAM table is translated and sent to amotion controller as a .lcn file over a USB connection. The mediageometries file utilized by the LSINC HMI allows it to send commands tothe INX HMI through the DLL file during printing to vary ink pressuresto compensate for inkjet head movements during printing. Hence, as maybe understood, the combination of the image file holding the graduatedmasking layer and a geometry file constitute a unique recipe for theprinting of an image onto the surface of the media object 51. Thatrecipe information is held by the PC 143 in its storage 148 and thecombination of the LSINC HMI and the INX HMI utilize that recipe toexecute each print job.

Print engine 149 includes an ink delivery system 144 that controlsmonitoring of ink levels in various containers in machine 10, pressurewithin ink tubes for consistent delivery of ink from tank to tank, andpressure delivered to the individual print heads. Engine 149 controlsthe drivers 153 for each print head and appropriate print head nozzlefiring responsive to the requirements of each print job. Engine 149 alsocontrols the generation of color ink signals to each print head toexpress each image color at the appropriate position on the media objectsurface as it rotates and moves laterally past the print heads.

System engine 145 provides top level system control of motion subsystem170 (see FIG. 13) which controls the motion of the media held by itscarriage, and all elements for printing and curing an image printed ontothe surface of media 51 loaded into machine 10. The PC 142 controls theLSINC HMI communicating the status and available commands to humanoperator 152, runs the software portion of the print engine, anddisplays the HMI via display and keyboard arrangement 151 forinteraction and for command inputs, and other data, to be sent to thehardware portion of the print engine 149.

Referring now to FIG. 13, it may be seen a function diagram showing theflow of control signals between various elements of the motion controlsubsystem 170 of the printing system 10. Subsystem 170 includes acollection of encoders functionally connected to a collection ofmovement means (e.g. 188, 186, 182, and 197), sensors (e.g. 177, 199),and controllers or “drives” (e.g. 187). The elements shown in FIG. 13are functionally depicted, but are also generally shown for illustrationpurposes in their spatial position relative to one another. As is known,each drive may be implemented as a separate PCB and include its owndevelopment tool kit that enables controller code to be created andstored in non-volatile memory of each drive board during systemoperation. The use of an EtherCAT compatible drive presents motor anddrive as a servo axis that can be managed via standard EtherCATprotocol. Movement means consist of either DC stepper motors orsynchronous servo motors, and are driven by dedicated driver boardscontrolled by controller 191. Communication between each driver boardand controller 191 is accomplished via a plurality of communicationcables 174 using standard EtherCAT protocol connected via EtherCAT PCB179 that allows for an update time of at least 2 ms between elements. Inthe preferred embodiment, 46 axes are maintained simultaneously in thesystem 170, with a 2 ms response time which is sufficient to achieve anoperative system using this number of axes.

Each movement means includes an encoder to ensure continuous feedback asto axis position in the system 170, and to ensure movement compliancewithin a bounded position set. Each electronic movement subsystem usessensors and encoders to provide closed-loop feedback as to the positionof any axis relative to media object 51.

As shown, print head manipulators 71 includes a series of electronicmovement control subsystems 180 having a Z-axis drive, Z-axis offsetdrive, and an X-axis drive 187, each with their own set of home sensorsand limit switch sensors 177, and a linear actuator with encoder 188.Each subsystem 180 is required for each manipulator 71, which incombination together make up a bank of manipulators 29 (see FIG. 2B). Inthe preferred embodiment, system 170 includes 12 of subsystems 180, onefor each print head 72, but print system 10 may work with more or lessthan 12 print heads depending upon the number of colors required foreach print job and the time in which each print job must be completedfor manufacturing goals. For example, an increase in print heads wouldincrease the machine's capacity for high volume manufacturing. Hence,system 170 is scalable for a particular machine to meet a particularprinting application requirement.

An X-axis movement for object 51 is accomplished with subsystem 189having a drive unit 181, a linear motor 182 and encoder 183, and homesensor 177 and limit switch 178. An optical encoder 194 (not shown) ispositioned adjacent to tail stock spindle 59 to provide positioninformation on media 51 position along path 68 to provide a closedposition feedback loop with X-axis drive 181. An entry sensor 192 andlight curtain sensor array 198 provide additional feedback to controller191 for operator and machine safety. Subsystem 189 is connected tocontroller 191 via EtherCAT communications line 174. Rotary movement ofmedia 51 occurs via rotary axis subsystem 184 having a drive unit 185 ona PCB, a motor 186 and position sensors 192. X-axis subsystem 189 isconfigured so that linear motor 182 is a slave relative to rotary axissubsystem 184, rotary motor 186, and all print head subsystems 180 areslaves relative to linear motor 182. This slave arrangement facilitatesthe use of a CAM table (see FIGS. 14A-14B) to control the relativepositions of the elements shown in subsystem 170 and allows for acontinuously varying ratio of movement elements to achieve satisfactoryprint head movement to follow object contour surface 121 through slopedareas 102. Prior systems utilize direct gearing arrangements and cannotvary movement of elements in continuously varying ratios, and thereforecannot follow contoured paths even if they were arranged to be capableof physically moving in a 3-dimensional manner to follow those contouredpaths at different resolutions

Each curing lamp assembly 62 in bank 60 (see FIG. 6) includes anelectronic subsystem 190 similar to print head subsystems 180. Eachsubsystem 190 includes a drive unit 196, an actuator 197 with encoder,and four sensors (home, limit, front, and rear) 199. Lamp subsystems 190are connected to controller via EtherCAT cable 174 as shown. Bank 60preferably includes 7 subsystems 190, one for each UV lamp, but as withthe print heads are scalably arranged to accommodate less or more lampsthan 7, depending upon the machine operational requirements.

Through cable 174 and EtherCAT control board 179, motion controller 191commands the individual drives through the EtherCAT protocol to controleach movement means, thereby providing coordinated movement of allelements in subsystem 170. For system level movement coordination, anencoder PCB 193 ties timing signals between print engine 149, inkdelivery system 144, and motion control subsystem 170 via cable 172. Anoptical encoder 194 residing on the rotary axis 185 provides timing firepulses to encoder PCB 193 which distributes the same signal to themotion control system 170 via cable 174. Rotary axis PCB 192 conditionsthe signal and simultaneously passes it to the head drive controllers ofprint engine 149. This allows for the system 10 to communicate the Xposition of media 51 as it travels along path 68 within print area 17.

Satisfactory off-the-shelf components for sub-system 170 shown in FIG.13 are listed in Table 1.0 below:

TABLE 1 FIG. 13 Element No. Element Name Mfg./Part No. Description 182X-axis Linear Motor Parker Automation/406T14LXRMP Linear Motor 181X-axis Linear Drive Kollmorgen/AKD-P00:306-NBEC- Drive Unit 0000 183X-axis Linear Encoder Integrated with Linear Motor Integrated Encoderwith home and limit switch in motor 186 Rotary Axis Motor Kollmorgen/PN:AKM23D-EFGNC- Motor OO 185 Rotary Axis Drive Kollmorgen/PN: AKD-P00306-Drive Unit NBEC-OOOO 192 Rotary Axis Encoder Renishaw/PN: T10100A-40E191 Motion Controller Trio Motion Technology LLC/PN: Quad Core uP w/PB62 & P914 support up to 64 Remote P862 + PB78 + 5x P914 Axes 187 andLinear Actuator (head Thomson/PN: with 4k ppr differential 197 & lampmanipulators) MLUA051S 1B-0100-03000SFSS- encoder (use ″FAS for x- 001axis, w/anti-backlash nut, 1.3 inch lead, no encoder) 188 and LinearActuator Drive RTA/PN: CST ET Model 94 Drive Unit 196 (head and lampmanipulators) 177 Limit sensor for home Panasonic/PM-25/45/65 series u-Photo-electric sensor position & end of shaped micro photoelectricsensor travel position (head & lamp manipulators) 177 Head and LampCrash Panasonic/Ex-11B Sensor Sensors (front and rear)(head and lampmanipulators)  63 Curing Lamps Phoseon/Fire Edge FE400 Enhanced bodystyle 120 × 10AC 385 nm w/rod lens PN: with air filters & glass 33607protector 198 Safety Light Curtain 14 mm resolution, finger Dual Zone:operator Sensor protection; <50 ms response time station location andprint area termination

As indicated above system 10 relies upon an installed ink supplysubsystem purchased from Inx International, referred to herein as an“ink delivery system.” However, in order for system 10 to print imageswith consistent ink quality onto media surface 121, delivery of inkthrough print heads 72 requires modulation of the ink delivery system inorder to compensate for motion of print heads 72. In an industrystandard print system, ink delivery system 144 provides a static vacuumto a series of ink supply lines from ink reservoirs (not shown) held incabinets behind panels 13 to a plurality of ink containers 31 positionedproximate to and above ink head assemblies 29. Electronics held in bay26 control vacuum system assembly 27 to deliver ink from the inkreservoirs to tanks 31, and also to print heads 72 via a system of tubes(not shown). Each tank also has its own pressure line via one of themanifold fittings 88 that forces ink from tank 31 to the print head 72.While standard ink delivery systems use static pressure to delivery inkto print heads, the disclosed system 10 modulates the delivery of ink toeach print heads from each tank 31 to compensate for the change ingravitational forces applied against each print head 72 as each head isaccelerated and decelerated to conform to surface contour 102. Thatmodulation is achieved by sending pressure value alteration signals toink delivery system 144 generated by the INX HMI running on the PC via aUSB connection. The INX HMI is in turn responsive to the LSINC HMIsending pressure offset values via DLL commands to the INX HMI, whichare responsive to derivative values from print head movements 74,76, and86 (see FIGS. 7A-7B). Those derivative values are known ahead of timeand predetermined during the calculations to create the CAM table 200(see FIGS. 14A-14B). For example, as print head 72 moves down, inkvacuum pressure must increase to compensate for the increased statichead pressure due to gravity forces on the ink delivery system and viceversa as the head moves upwards. The motion control system maintains therelative position of the heads from a home position. The optimalpressure settings in mBar are determined at the home position viacalibration testing that ensures the heads do not weep ink. Based on thedensity of each respective ink used, a revised pressure value iscalculated in mBar based on its distance from home in millimeters andthe ink's specific gravity. The pressure value is calculated using thefollowing formula:Pressure at position=Pressure at home+(distance traveled from home inmillimeters)×(specific gravity of the ink/relationship between mmH20 andmBar of 10.197mBar/mm)This information is communicated via a USB bus connected to the inkdelivery system 144 (e.g. the JetINX's ink delivery system) every 25 msor less if the values change. If the values do not change then norefresh signal is required.

Referring to FIGS. 14A-14B, it may be seen a CAM table example 200 basedon a print job profile 143. CAM table 200 is truncated 224 since thefull extent of values is unnecessary for a full understanding of thefigure. CAM table 200 includes a series of columnated values 201 thatcontrol movements of various servos and actuators shown in motionsubsystem 170 and which were calculated based on the formulas used todescribe the movement mechanics of FIG. 11. Each row of numbersrepresents a discrete position and movement condition for all movementmeans described for motion control subsystem 170 described in FIG. 13along print path 122. Column A 202 holds values representative of thegeometry of the media object 51 as recorded in a CAD program that wasused to model the object, and holds the distance from axis 107 for anymodeled object in millimeters and is equivalent to R_(i). Informationfor Column A may be obtained in various known ways, such as manualmeasurements taken along the object surface to calculate its diameteralong its surface from which R_(i) may be derived. The object may bescanned and seed values in the CAD program used to calculate the values.Or, the CAD program itself may calculate the values and output atabulated list of values based on entered user parameters for the CADsoftware program. The resolution for the values of A are at most ±0.001mm. Column B 203 holds slope values calculated for the slope along eachpoint recorded from Column A and are readily provided by most CADprograms. Column C includes the rate of change for each slope value fromthe prior entered slope value. Columns D-G include values pertaining toZ_(i), such as D 206 offset print head curve values 122, E 208 velocityof the print head in millimeters per second at the corresponding pointin Column A, F 211 required print head tilt position 74 (see FIG. 7A) inmillimeters, and the corresponding required tilt velocity G 212millimeters per second. Values held in columns H-J pertain tocompensation movements of each manipulator assembly 71 (see FIGS. 7A-7B)such as H 214 the required horizontal shift at each point along theprint path in millimeters, the cumulative derivative shift along thecurve in the print path I216, and the a D_(x) correction offset value inmillimeters J 217. The Dx correction offset maintains a constantvelocity relative to the target print surface. Column K 219 holds thelamp path value in millimeters along which the path UV lamps traversesrelative to axis 107.

CAM table 200 is held in PC storage 148 and motion controller 191retrieves the values and stores them in its non-volatile memory upon theoperator 152 initiating the printing process through the HMI. The printhead positions are slaved to the motion of the linear motor 182 (seeFIG. 13). The position of each stepper axis is represented as a CAMtable driven by the position of the linear motor 182. As may beunderstood, row values from 1−n 222 comprise the complete movementvalues required to complete any print job.

In operation, an operator will use a third-party software CAD program todescribe and produce table 200, while exporting the graphic file for thedesign to be printed into a format acceptable for printer ripping. Theripping tool will then generate a printer specific file representing theimage to be printed and a gradient mask calculated based on the mediaobject geometries and recorded in a geometry file. The printer specificfile (.isi) and geometry files (.lsg) for the media object to be printedare then transferred via a thumb drive or other common transferencemethod to Windows PC 142 along with all necessary support files asrequired by print engine 149. The object to be printed (i.e. the mediaobject 51) is loaded by the operator 157 onto spindle 52 a,b with axis107 of the object properly aligned with the rotational axis of spindle52 a,b. Using the HMI on the Windows PC display 151, the operator 152then moves carriage 57 holding the spindle 52 a,b and object 51 into theloading area 18. Inks suitable for the object surface print job arepreloaded in machine 10 and ready for use as is known. The print job isthen initiated and the object 51 spun at a predetermined rotation rateand ink applied onto the object surface at the correct rotationallocation along print path 122. Carriage 57 holding the object 51 movesalong distance Y_(0−i) 114 at a constant velocity 127 as ink isexpressed against surface 121 from each print head 72. Responsive tomotion control signals issued by controller 191, and as synchronizedwith print engine 149 via encoder PCB 193, each print head assembly 71moves print head 72 into position in a spaced and parallel relation tothe surface 121 of the object as object 51 is moved along path 122,applying ink at the precise location along the object surface. As isunderstood, each print head color is overlapped in a coordinated fashionat the same location on the object's surface so that predeterminedcolors are achieved on the objects surface to create the preloadedimage. Individual UV lamps 63 held in curing lamp bank 60 are moved upand down to conform in a spaced relation to object surface 121underneath rotating object 51 as it progresses along path 122, therebycuring ink applied to the surface of object 51. Once the object has beenprinted and end of print distance 114 reached, the object is returned tothe home position and withdrawn by operator 152 from the loading area18. The process may then be repeated for further objects to be printed,except that the print job profile generation and file loading steps maybe omitted if the object to be printed is the same as the previousobject and the image is the same.

While I have shown my invention in one form, it will be obvious to thoseskilled in the art that it is not so limited but is susceptible ofvarious changes and modifications without departing from the spiritthereof.

Having set forth the nature of the invention, what is claimed is:
 1. In conjunction with a direct-to-shape printing system having a frame, an ink delivery system supported by said frame capable of drawing ink from a plurality of ink reservoirs and delivering a color image to a plurality of inkjet printing heads to produce a printed image on a media object surface, wherein each said print head is capable of moving in 3-dimensions of space in order to follow a contoured surface over said media object, said ink delivery system controlled by a computer system capable of receiving user control inputs and print directions based on a print profile for said media object, a method for modulating ink pressure to said plurality of inkjet printing heads, comprising the steps of: a. responsive to the type of ink utilized in the printing system, calibrating a home pressure for at least one print head positioned at its home position such that said inkjet heads encounter a maximum pressure in said ink delivery system of said ink without weeping ink at a resting position and recording the pressure at that condition; and, b. during printing, modulating the ink pressure based on said home pressure setting to each said print head to compensate for gravity forces at each said print head responsive to contour following movements of each said print head over said media object.
 2. The method as recited in claim 1, wherein said step of modulating said ink pressure is determined by calculating a new pressure at any print head position during printing, wherein said new pressure at said position comprises: pressure at said home position+(distance traveled from said home position in millimeters)×(specific gravity of the utilized ink in mBar/mm); and, wherein the pressure at said home position is the pressure calculated in said step of calibrating a home pressure for at least one print head.
 3. The method as recited in claim 2, wherein said step of modulating said ink pressure includes the step of said computer system calculating pressure modulation values based upon a CAM table created from geometries based upon said media object shape.
 4. The method as recited in claim 3, wherein said step of modulating ink pressure occurs at a sampling rate of at least every 25 ms separately for each inkjet head while each said inkjet head is moving.
 5. The method as recited in claim 4, wherein said step of modulating ink pressure is based on precalculated derivative values of anticipated speed during movement of each print head when printing over said media object.
 6. The method as recited in claim 5, wherein said step of modulating ink pressure occurs by said computer system sending a signal via a USB bus to said ink delivery system.
 7. The method as recited in claim 1, wherein said step of modulating said ink pressure includes the step of said computer system calculating pressure modulation values based upon a CAM table created from geometries based upon the shape of said media object.
 8. The method as recited in claim 7, wherein said step of modulating ink pressure is based on precalculated derivative values of anticipated speed changes during movement of each print head when printing over said media object.
 9. A method for modulating ink pressures in an ink delivery system in a direct-to- shape printing system comprising the steps of: a. using a computer processor to calculate print head positions of a print head movable in 3-dimensions of space to conform to an axially symmetrical, contoured exterior surface of a media object to be printed upon; b. calculating the derivative values of the speed of movement of said print head for each print head in said printing system for said media object; and, c. based upon said calculated derivative values, modulating the ink pressures delivered to each print head during printing to compensate for gravity forces at each said print head responsive to contour following movements of each said print head moving over said media object.
 10. The method as recited in claim 9, further including the steps of: a. responsive to the type of ink utilized in said printing system, calibrating a home pressure for at least one print head positioned at its home position in said printing system such that said inkjet head encounters a maximum pressure in said ink delivery system of said ink without weeping ink at said resting position; and, b. and recording said home position pressure at that condition.
 11. The method as recited in claim 10, wherein said step of modulating said ink pressure is determined by calculating a new pressure at any print head position during printing, wherein said new pressure at said position comprises: pressure at said home position+(distance traveled from said home position in millimeters)×(specific gravity of the utilized ink in mBar/mm); and, wherein the pressure at said home position is the pressure calculated in said step of calibrating a home pressure.
 12. The method as recited in claim 11, wherein said step of modulating said ink pressure includes the step of said computer processor calculating pressure modulation values based upon a CAM table created from geometries based on said media object.
 13. The method as recited in claim 12, wherein said step of modulating ink pressure occurs at a sampling rate of at least every 25 ms separately for each inkjet head while each said inkjet head is printing.
 14. The method as recited in claim 13, wherein said step of modulating ink pressure is based on precalculated derivative values of anticipated acceleration resulting from movement of each print head over the surface of said media object.
 15. The method as recited in claim 14, wherein said step of modulating ink pressure occurs by said computer processor sending a signal via a USB bus to said ink delivery system.
 16. The method as recited in claim 9, wherein said step of modulating said ink pressure to each print head includes the step of calculating a new pressure at any print head position during printing, wherein said new pressure at said position comprises adding a calibration pressure for a selected one of said print heads at said a home position to the distance traveled from said home position in millimeters multiplied times the specific gravity of the utilized ink in mBar/mm.
 17. The method as recited in claim 16, wherein said step of using a computer processor to calculate print head positions of each print head and said precalculated derivative values used in said step of modulating ink pressure based on said precalculated derivative values both use a personal computer to accomplish such calculations, and wherein said personal computer is positioned within said direct-to-shape printing system.
 18. In conjunction with an ink delivery system capable of drawing ink from a plurality of ink reservoirs and delivering a color image to a plurality of inkjet printing heads to produce a printed image on a media object surface, said ink delivery system controlled by a computer system capable of receiving user control inputs and including a series of ink pumps and manifold pressurized tanks proximal to said inkjet printing heads, a method of printing in a direct-to-shape printing system capable of varying ink pressures to each inkjet print, comprising the steps of: a. pressurizing each manifold pressurized tank to a maximum pressure at which ink at each print head will not weep when said print head is at its resting home position; b. during printing of an image over the contoured surface of said media object, modulating the pressure to each print head to a new pressure as it prints over the surface of said media object calculated in accordance with the following formula: i. new pressure=pressure at said home position+(distance traveled from said home position in millimeters)×(specific gravity of the utilized ink in mBar/mm); and, c. updating said new calculated pressure separately for each print head at a sampling rate of at least every 25 ms. 